Field of the Invention
The invention pertains to the field of variable cam timing phasers. More particularly, the invention pertains to a multi-mode variable cam timing phaser.
Description of Related Art
It has been demonstrated that operating a variable camshaft timing device phaser utilizing the camshaft torque energy to phase the valve timing device is desirable because of the low amount of fluid required by a camshaft torque actuated variable camshaft timing device. However, not all engines provide enough camshaft torque energy throughout the entire engine operating range to effectively phase the variable camshaft timing device.
BorgWarner's U.S. Pat. No. 6,453,859 discloses a phaser that uses cam torque and oil pressure to move the phaser. The phaser has a single recirculating check valve that either recirculates fluid to the advance port or the retard port. The single recirculating check valve is located downstream of the control valve and not connected directly to the advance and retard chambers.
Hilite's U.S. Pat. No. 7,946,266 discloses another phaser that uses cam torque and pressure to move the phaser. The phaser has two recirculating check valves prior to exhaust fluid entering the control valve or upstream of the control valve. A recirculating check valve is required for each set of chambers—advance and retard.